Recently, various kinds of electrographic apparatuses have widely been used in practice. In general, the electrographic apparatus makes use of a medium being charged such as a photoconductive body or a record sheet and a device for charging such medium being charged.
As such charge device, it has been the common practice to use a corona charge device.
It is preferable to make the corona charge device small in size and highly efficient in operation. For this purpose, however, each of constitutional elements of the corona charge device must be small in size and highly efficient in operation.
In an effort to make the practical corona charge device small in size and highly efficient in operation, one attempt has been made to employ a small type shield electrode. However, if the shield electrode is made small in size, it is impossible to operate such small type shield electrode as an ion supply source in a stable manner without producing any spark discharge for lack of the insulating characteristic of air.
In an effort to make the practical corona charge device small in size and highly efficient in operation, another attempt has also been made to reduce the diameter of a corona discharge wire. A tungsten wire having a diameter of the order of 30 .mu. to 100 .mu. has frequently been used as the corona discharge wire. If the diameter of the corona discharge wire is reduced, corona is produced at a low voltage, and as a result, the small shield electrode can be used without producing any spark discharge. But, since the mechanical strength of a thin tungsten wire is low, there is a risk of the thin tungsten wire being broken thus requiring much maintenance. In an effort to make the practical corona charge device small in size and highly efficient in operation, further attempts have been made to coat the corona discharge wire with material which can efficiently emit a flow of ions or deform the corona discharge wire into a structure which is not rectilinear in form. All of these attempts, however, have the disadvantage that the use of such measures could not make the corona charge device stable in operation and less expensive.